The present invention relates to an oven for heating, cooking and baking food products including a radiant panel which is heated by a stream of moving air to thereby supply heat energy to a food product by means of radiant energy. The invention furthermore relates to an oven for preparing a food product wherein it is desirable for one surface of the food product to be heated at a first energy input rate and a second surface of the food product to be heated at a second energy input rate, wherein the second rate is greater than the first rate.
In restaurants and other food preparation establishments, particularly fast food restaurants, the speed at which certain foods, such as pizza, can be prepared is extremely important. Both the restaurant operators and diners prefer that the food be prepared in a very short amount of time, but that the quality of the food not suffer because of the short preparation time. Certain types of food are best prepared when the rate of heat energy input into one surface of the food product is different than the rate of heat energy input into another surface of the food product. This is particularly true with a food such as pizzas, which have become very popular fast food items. Pizzas normally have a crust, a filling composed of vegetables, meats and cheeses and a top layer of cheese onto which may be placed a variety of toppings. Thus, the top surface of the pizza requires that a limited amount of heat energy is imparted thereto so that the cheeses will melt, and after baking will have a milky white appearance with just a small amount of browning. At the same time, the crust, or bottom surface of the pizza, must be brown. Certain pizza products which have become very popular are referred to as "deep dish" or "stuffed" pizzas, which have a greater thickness than conventional pizzas and therefore require a greater amount of heat energy input. However, a smaller amount of heat energy should be supplied through the top of the pizza than through the bottom of the pizza because the application of a large amount of heat to the top surface tends to cause the cheese to burn, and will also cause certain toppings, such as thinly sliced onions to scorch. Accordingly, pizza products, and in particular very thick pizza products, require that the rate of heat energy input into the top surface be lower than the rate of heat energy input into the bottom surface thereof.
Other food products also benefit from heat being applied thereto during baking at two different rates for the top and bottom surfaces. For example, when baking sheet cakes, the batter is typically contained within an open top metal pan. It is desirable that the heat energy input into the batter be controlled in such a way that the cake will not begin to bake prematurely at one end of the pan, thereby resulting in drifting of the batter which produces an uneven cake.
An apparatus and method for successfully preparing food products, such as pizzas, is described in U.S. Pat. No. 4,154,861. This patent discloses an impingement process wherein a conveyor belt travels through an oven cavity and on which the pans containing the pizzas are located. Columns of hot air are directed at localized areas of the pizza to bake the pizza and to carry away moisture and other particles resulting from the cooking process. This method and this type of oven has been used successfully by pizza establishments for a number of years. However, if this basic type of oven were used with stuffed types of pizzas or pizzas having delicate tops, the tops of the pizzas can be burned while the inner portion of the pizza and the crust would not yet be properly baked.
U.S. Pat. No. 4,462,383 discloses an impingement oven for preparing foods wherein a pair of duct fingers is provided, each finger having a jet plate through which hot air is vented in standing columns to impinge on food products located in an oven cavity between the duct fingers. The food travels on a conveyor belt through the oven cavity between the duct fingers as it is being cooked.
If the temperatures in the impingement ovens of the type discussed above are lowered so that the top surfaces of the food products would not burn, the temperatures in the oven would be too low to effectively bake or cook the inside of the product, such as a pizza product, in the desired amount of time. It is therefore desirable to provide an impingement oven wherein the heat energy supplied to the bottom surface of a food product, such as a thick pizza, is greater than the heat energy which is supplied to the top surface thereof.
In the case of certain baked food products, such as sheet cakes, the use of a conventional impingement oven will often cause non-uniform baking. As the pan containing the batter moves by conveyor into the oven, the leading edge thereof is subjected to columns of high temperature air, which immediately cause the batter to begin to bake and rise. This rising of the baked batter displaces unbaked batter toward the trailing end of the pan, thereby causing batter drift which results in an uneven cake with the leading portion of the cake being thinner than the trailing portion thereof.
U.S. Pat. No. 4,591,333 discloses a prior art oven including radiant panels which are positioned above the conveyor and impart heat to the food product by means of infrared radiation. Such infrared radiation imparts heat at a much lower rate than columns of impinging air, which are directed to the food product from impingement finger ducts located below the conveyor. In one embodiment of the oven disclosed in U.S. Pat. No. 4,591,333, conventional impingement fingers are blocked off by means of highly thermally conductive radiant energy plates, which deflect the impinging air laterally and upwardly away from the food product, yet includes an emissive outer surface which, when the panel becomes heated, radiates infrared energy toward the food product. In a second embodiment, the apertured lower plate of the impingement finger is replaced by a solid emissive radiant panel having corner apertures to permit pressurized air to escape the duct and be drawn back into the plenum.
Although the oven disclosed in U.S. Pat. No. 4,591,333 has been successful in enabling a lower amount of heat energy to be applied to the upper surface of a food product than is applied to the lower surface thereof, it has been found that there are certain aspects of the oven which can be further improved upon. For example, since the air escaping from the upper radiant panel ducts is directed upwardly rather than downwardly as is the case in a conventional impingement oven, hot air tends to collect in the upper portion of the cavity thereby raising the temperature of the upper portion of the cavity. Furthermore, the radiant panels are rigidly connected to the duct fingers, and if the radiant panels are of a different material than the duct fingers, the differing rates of thermal expansion can in some cases result in warpage. For example, if the duct fingers are made of stainless steel, which is a common material for commercial food processing equipment, and the radiant panels are made of highly conductive, anodized aluminum, the rates of expansion between the duct fingers and panel will be different.
U.S. Pat. Nos. 4,154,861; 4,462,383 and 4,591,333 are incorporated herein by reference.